Monte Carlo Simulation of Plasma Etch Emission Endpoint

As dry etch requirements become more severe, the trend is toward greater automation of the etch process. Automated endpoint detection is desireable to prevent excessive substrate damage and to increase etch reproduceability. The challenge in designing an automated endpoint detector is to provide a unit with sufficient intelligence to correctly recognize etch completion despite wafer non-uniformity and wafer to wafer variations. In this paper a simple, easy to implement simulation program based on Monte Carlo techniques is described which can be used to study the effect of wafer thickness and etch rate uniformity on the emission endpoint transition. A version of the program which incorporates loading effects is also demonstrated. The loading effect is shown to increase the abruptness of the endpoint transition. The simulation is compared with actual emission data for nitride and polysilicon etching in a commercial single wafer plasma etcher.